The present invention relates to a coating solution which provides an anti-reflective, planarizing layer for use in photolithography processes in the production of semi-conductor devices. This layer can function as a hard mask for plasma etching since it has an etch rate lower than that of conventional photo resists.
Increasing demand for faster integrated circuits have made imperative the development of devices with multi-level metallization layers. These developments necessitate utilization of layers of planarizing material to smooth uneven topography on the substrate so that there will be minimum thickness variation in the subsequent layers, such as a layer of photoresist material. The need to provide uniform layers of resist material increases as the device dimensions shrink.
The topography of an underlying substrate can cause optical interference in the photolithography process by reflection of the photons. Anti-reflective coatings have been used so as to prevent interference from the reflection of the irradiating beam. It is conventional to incorporate a dye into the anti-reflective layer to prevent loss of resolution resulting from substrate reflection.
In conventional processes, separate layers provide planarization and anti-reflection. Organic planarization layers are typically used in photolithography techniques since the planarization layer must achieve good pattern transfer from the top photoresist layer. Fuller et al., U.S. Pat. No. 4,557,797 disclose the use of a polymethylmethacrylate planarization layer. Pampalone et al., U.S. Pat. No. 4,621,042 discloses the use of an orthocresol novolak resin for planarizing a semi-conductor surface. Because it is often difficult to solubilize a suitable dye within the organic planarizing layer, a separate layer containing a dye is used as the anti-reflective coating. Organic compositions containing a dye are typically used to provide anti-reflective coatings.
It is desirable to provide a composition which will produce a layer that both planarizes and absorbs light.
Spin-on-glass compositions have been used as planarizing layers for other processes, such as the insulating layer between the metallization circuitry. The composition is applied to a semi-conductor wafer, spun and dried to form a solid layer that is subsequently cured at high temperatures to form a hard silica-based (glassy) layer. Despite various formulations for the spin-on-glass compositions, a number of limitations exist with respect to the production and use of most spin-on-glass compositions. Problems of surface damage from subsequent processing, poor adhesion and short shelf-life, among others have limited the utility of these compositions as planarizing layers. Limitations on thickness are also recognized due to the brittleness of the spin-on-glass layers.
A further limitation on spin-on-glass compositions as planarizing layers for photoresists is that it is difficult to control the plasma etch rate of the layers produced. This can result in the formation of recesses and losses in pattern resolution when transferred from a top layer of photoresist to an underlying metallization layer.